In the eye, the cavity between the lens and the retina is filled with a clear, jelly-like substance termed the vitreous body, vitreous humor, or vitreous. Its volume is fixed and is relatively permanent. The vitreous humor is 99% water, with most of the remaining 1% composed of salts (sodium, chloride, bicarbonate, etc.), collagen, and hyaluronan (hyaluronic acid). The collagen and hyaluronan give the vitreous is gel-like consistency and high viscosity. The outer surface of the vitreous is normally weakly adherent to the retina and ciliary body, with a somewhat tighter attachment at the macula, at the far periphery of the retina near the ora serrata, and at the pars plana of the ciliary body. In pathological conditions such as rhegmatogenous retinal detachment, macular hole, vitreomacular traction syndrome, and proliferative vitreoretinopathy, the attachment of the vitreous to the retina mediates or facilitates damage to the retina. For example, as the vitreous ages, its collagen contracts (a process called vitreous syneresis), and the contraction can produce traction on the retina ultimately inducing a tear or hole in the retina and a consequent retinal detachment or macular hole. As another example, the attachment may serve as a scaffold for fibrous, fibrovascular, or fibroglial proliferation emanating from the retina, a process called proliferative vitreoretinopathy. The fibrous membranes in proliferative vitreoretinopathy can contract and cause retinal tears, retinal holes, and retinal detachments, all of which can lead to blindness.
A patient suffering from these and some other vitreous-mediated diseases may benefit from a surgical procedure known as a vitrectomy. Vitrectomy can also be step in the process of other types of retinal surgery. Examples include the vitrectomy that typically accompanies the removal of foreign bodies that may have entered the vitreous body traumatically or iatrogenically, or the vitrectomy that accompanies the injection of a gene therapy vector under the retina, or the vitrectomy performed in eyes with infectious endophthalmitis to remove microorganisms and make space for the injection of antibiotics. However, the surgical procedure of vitrectomy itself can produce complications.
Many surgical procedures of the retina, such as the removal of epiretinal membranes, require complete dissection of the vitreous away from the retina to be optimally efficacious. The transparency of vitreous makes it challenging for the surgeon to visualize and hence completely remove the vitreous. A surgeon performing a vitrectomy may not be absolutely certain whether the posterior surface of the vitreous (called the posterior hyaloid) is completely separated from the retina and whether a complete vitrectomy has been achieved. While the surgeon attempts a complete removal of the vitreous near the retina, he or she may inadvertently cut into the retina and thereby create iatrogenic retinal defects or holes or possibly remove irreplaceable neural elements essential for vision. Many surgical techniques have been described which attempt to aid the surgeon in the removal of the posterior hyaloid during vitrectomy. These include the use of various cannulas, forceps, or vitreous-cutting devices with active or passive suction applied to engage and separate the posterior hyaloid from the retina. Ryan et al. have described the use of injected autologous blood for improved visualization of cortical vitreous during posterior hyaloid separation. None of these is completely satisfactory. For example, the instillation of blood into the vitreous has several drawbacks: blood disperses into the vitreous cavity and is likely to obscure visualization of the retina during vitrectomy, and it has the potential of causing postoperative inflammation and proliferative vitreoretinopathy.
In summary, iatrogenic damage to the retina is still a recognized potential complication of vitrectomy. A need still exists for a method to surgically remove the vitreous with improved accuracy, precision, and completeness so that complications, as well as discomfort, inconvenience, and expense to the patient, may be minimized. Thus, methods and agents to improve the visualization of the vitreous during a surgical procedure, and hence to ensure the accuracy of the procedure, are desirable to achieve better functional and anatomical outcomes.